There are many processes In industry in which it is desirable to "react" (chemically or physically) a slurry or a liquid with a gas. Of course most of such processes differ significantly in detail, but many processes have in common the desire to provide intimate contact between the gas and the slurry particles, or the liquid, and at a rapid rate. Rapid intimate contact results in the most effective reactions, and the fastest reaction rate, both desirable goals.
According to the present invention, these desirable goals are achieved for a wide variety of reactions between gases and liquids or slurries. According to the invention, gas is introduced into the liquid or slurry while it is in a vortex which may be, but is not necessarily, a vertical axis vortex, preferably in the form of small bubbles. The small bubbles--having a very high surface area to volume ratio--encounter a high pseudo-gravitational field generated by the rotation of the slurry or liquid in the vortex, and under the influence of the field the bubbles move toward the center of the vortex. Mass transfer from the bubbles through the air/liquid interface, through the liquid medium, into reaction sites on the solids surface (in a slurry), or to reaction sites on the liquid itself, is very rapid. It is rapid due to the large interfacial area, high degree of agitation due to rapid and continuous movement of the bubbles through the shear planes formed by the liquid phase in the vortex, the large number of bubbles, and the close proximity between gas bubbles and solid particles or reactant liquid. Gas (if any) to be discharged after the reaction is removed from the top portion of the vortex (if vertical), while the treated slurry or liquid is removed from the bottom of the vortex (if vertical). Under some circumstances, gas can also be removed from liquid adjacent the bottom of the vortex.
Typical processes to which the general method according to the invention is applicable include effecting chemical treatment of solids in a slurry with a gas chemically reactive with the slurry solids, chemically reacting a liquid with a gas, stripping a strippable component from a liquid utilizing a stripping gas, and absorbing a gas with an absorbable component in an absorbent liquid. In each case it is desirable to utilize a gas porous surface of revolution (e.g. cylindrical or conical) wall surrounding the vortex, and to practice the step of introducing the reactive gas into contact with the slurry or liquid through the gas porous wall.
A particular method of effecting chemical treatment of solids in a slurry with a gas reactive with the slurry solids, according to the invention, is treating paper pulp (comminuted cellulosic fibrous material slurry) with an ozone containing gas, such as ozone mixed with oxygen containing gas. The slurry may be introduced at a pressure of about 10-30 psig, while the gas is introduced at a pressure of about 2-10 psig. The gas porous wall may have pores with a pore size of 1-200 microns. Typically the slurry of comminuted cellulosic fibrous material has a solids concentration of about 1-3%. The residual gas removed may be acted upon to separate entrained droplets from the gas, condensing the gas to remove water vapor, effecting catalytic conversion to remove entrained reactant byproduct gases, effecting absorption to remove reactant byproduct gases, or generating ozone by passing the residual gas through an ozone generator. After discharge the slurry may be deaerated. Two or more vortices may be provided in series, with the pulp discharged from the first being fed to the inlet of the second, and with the residual gas withdrawn from the second being fed to the first as the reactant gas.
Chemical reaction between a slurry and gas may also be provided, according to the invention, by scrubbing flue gas having sulfur compounds or nitrous oxides with a calcium carbonate slurry. In such a case a series of vortices is typically provided, the first vortex (as far as flue gas flow is concerned) having a large pore gas porous wall (e.g. about 1-5 mm).
For that aspect of the invention in which a liquid is reacted with a gas, various liquids and gases typically used in the pulp and paper making field are particularly suitable, although the invention has much wider applicability. For example chlorine or chlorine dioxide gases can be reacted with caustic solutions, sulfur dioxide solution, or spent alkaline bleaching plant liquor during the scrubbing of a bleach plant exhaust. Air or oxygen can be used to oxidize kraft mill white, green, or black liquors.
The invention is applicable to a wide variety of liquid components strippable from a liquid, utilizing a stripping gas. For example water vapor may be stripped from hot or warm water using air, to produce cooler water. Black liquor soap may be stripped from black liquor using air.
The practice of the method according to the invention for absorbing a gas with an absorbable component in an absorbing liquid also has wide applicability, including in the pulp and paper field. For example the invention may be practiced to effect condensation, or to dehumidify air by the contact of warm water vapor and air by cooler water. Mists of various types, such as sulfuric acid droplets, may be absorbed in water or other solvents, and water or other desirable liquids can be utilized to absorb ozone, chlorine, chlorine dioxide, sulfur dioxide, carbon dioxide, or ammonia gases (either by themselves, or mixed with air or other gases ) .
In all of the methods according to the invention, additives may be also added either to promote reactions (e.g. the addition of catalysts), or to promote mass transfer (e.g. surface active agents to improve bubble stability).
It is the primary object of the present invention to provide for the effective mixing of gas in a slurry or liquid, to produce a wide variety of desirable end results such as chemical reaction, stripping, absorbing, or the like. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.